Background Geriatric patients experience more adverse events owing to early complications after TKA or THA related to preexisting comorbidities. However, associations between patient and surgery variables, including age, BMI, and comorbidities with complications are unclear. Knowing these relationships is necessary for developing risk stratification, defining contraindications, and predicting complications and adverse outcomes.Questions/purposes We wished to establish and quantify the associations among age, BMI, comorbidities, and type of surgery and anesthesia with complications and early adverse outcomes including longer length of stay, disposition to an extended care facility, readmission, and reoperation in geriatric patients undergoing TKA and THA. Patients and Methods We prospectively followed a cohort of patients older than 65 years undergoing TKA or THA. Demographics, comorbidities, complications, discharge disposition, readmission, and/or reoperation information within the 90-day postoperative period were collected. Adjusted hierarchical stepwise multivariable regression models were used to analyze associations and relative risks with complications, length of stay, disposition, readmission, and reoperation rates.